Dr Mark McLean, Geological Survey of Victoria presents a talk titled A new Full Spectrum FALCONⓇ airborne gravity and aeromagnetic survey over the Otway Basin, Victoria.
Tickets here
Our next meeting will be a joint event with the Young Professional Group and will happen on the 1st of October 2019. As usual it will be held at the Kelvin Club from 6 pm onward.
We will have the pleasure to welcome Dr Mark McLean from the Geological Survey of Victoria with a presentation about the Falcon survey that was acquired recently in the Otway Basin.
Please register before the 30/09/2019 noon time using the Eventbrite link.
In case of dietary requirement please email directly to vicpresident@aseg.org.au.
Abstract
Seismic surveying has been demonstrated to be the most effective technique to image sub-surface geological structure, particularly within sedimentary basins characterised by sub-horizontal stratigraphy where seismic energy is readily reflected back to the surface. However, there are some examples where seismic acquisition does not provide the most effective results: 1) where the area of interest lies along the coastal transition zone making acquisition problematic, 2) where there are sub-vertical geological structures (such as faults) which cause the seismic energy to be reflected away from the sensors and 3) where volcanic rocks attenuate the seismic signal.
Airborne Gravity Gradiometry (AGG) is a technique which measures very small changes in Earth’s acceleration. This approach is appropriate for the Otway Basin particularly in the transition zone where the geology is poorly understood. Qualitative interpretations can be made in map view, but data can also be quantitatively modelled using forward and inversion modelling processes. This approach makes airborne gravity gradiometry a complementary dataset for most of the seismic in the Otway which is dominated by 2D lines. Therefore, airborne methods provide an opportunity to not only ‘fill in the gap’ along the coast between seismic data collected off-shore and onshore, but there is also potential to add further detail to horizon geometries in between the more widely spaced (3-4km) seismic lines.
A new airborne Full Spectrum Gravity and magnetic survey has been undertaken as part of the Victorian Gas Program (VGP) using CGG’s FALCON® airborne data acquisition system. Flying commenced in August 2018 and was completed by early January 2019 (12 weeks). A total of 31042 line km of gravity, gravity gradiometry (Full Spectrum), magnetic and laser scanner data were acquired along 500 m spaced lines in a NW-SE orientation and 15000 m perpendicular tie lines. The surveyed region includes approximately 16000 km2 of the Otway Basin in Victoria, stretching from the edge of the Otway Ranges to the South Australian border, and from south of the Grampians to approximately 18 km offshore. Data were acquired at an altitude of 150 metres, increasing to 300 metres over built-up areas. A single engine Cessna Grand Caravan 208B was used to conduct the onshore portion of the survey and a DHC-6-100 (Twin Otter) aircraft was used for the offshore component. The survey has resulted in the largest airborne gravity dataset ever collected in Victoria and provides superior quality gravity imagery, compared with pre-existing data.
This presentation will visit a range of topics including the initial rationale for the survey, survey design, instrumentation and acquisition, but some emphasis will be placed on the new Full Spectrum product now being offered by CGG. This survey is the first publicly available Full Spectrum Falcon survey and is intended to capture the full spectrum of wavelengths by conforming the short wavelengths from the gravity gradiometry, with the longer wavelengths obtained from concurrently acquired conventional gravity.
Bio
Mark completed Arts/Science and Master of Science degrees at Monash University and then completed a PhD at The University of Melbourne in 2008 which involved acquisition, interpretation and modelling of an airborne geophysical survey over the Lambert Rift region in East Antarctica. Since then, Mark has worked at the Geological Survey of Victoria building regional 3D framework and rock property models using geological and geophysical datasets. Mark's time is now split between the GSV, and The University of Melbourne where he lectures in Applied Geophysics.
